The advent of an electronic trip unit for circuit protection has resulted in a sophisticated means of controlling the trip parameters by careful selection of overcurrent values and time overcurrent durations. Such circuits are capable of further providing ground fault circuit protection by the addition of ground fault sensing transformers and additional circuitry.
When undervoltage protection is required along with overcurrent protection some electromechanical undervoltage release means must be added to the circuit breaker in addition to the electronic trip unit. U.S. Pat. No. 4,301,434 in the name of Roger N. Castonguay describes one such undervoltage release reset and lockout apparatus for use with electronic trip units to provide undervoltage protection.
U.S. Pat. No. 4,408,174 in the name of Raymond K. Seymour et al. discloses a multifunctional mounting module for shunt trip, undervoltage and remote signalling by means of a common accessory mounting module for use with electronic trip units to provide a plurality of electromechanical accessory functions.
U.S. Pat. No. 3,693,122 in the name of Henry G. Willard discloses a flux transfer trip device for electronic trip units wherein the flux provided by a permanent magnet is opposed by a magneto-motive force produced by a solenoid winding. A flux diverter interposed between the permanent magnet and the spring-biased tripping armature provides instantaneous trip properties by effectively de-coupling the permanent magnet flux by operation of the solenoid winding. The Willard flux transfer trip device is currently used in combination with the aforementioned electromechanical accessory apparatus to provide remote tripping as well as undervoltage protection to the protected circuit.
An earlier attempt to provide an electronic trip unit along with undervoltage protection is described within U.S. patent application Ser. No. 674,451 filed Nov. 23, 1984 entitled "Bistable Undervoltage Release Circuit For Circuit Breakers" in the name of E. K. Howell. This circuit utilizes a bistable undervoltage release function whereby a first signal to a solenoid coil holds the armature against a spring force. A second signal of opposite polarity produces an opposing magnetic flux to cancel that retained by the solenoid. The armature becomes extended under the influence of the charged spring to trip the breaker. A control signal is developed within a sensing circuit to determine the presence of either undervoltage or overcurrent to operate the solenoid to trip the breaker upon command. U.S. Pat. No. 4,013,926 discloses a combined trip actuator and undervoltage release mechanism wherein the undervoltage coil and trip release coils are co-axially arranged relative to the solenoid plunger. It is believed that the present invention improves over the teachings of this patent by arranging the undervoltage coil with the solenoid plunger. This arrangement provides the required electrical immunity between the undervoltage and overcurrent coils. The aforementioned U.S. Patents and Patent Application are incorporated herein for purposes of reference.
The purpose of the instant invention is to disclose a flux transfer trip device having both undervoltage and remote trip facility within a common housing and which can be utilized with an electronic trip unit with only slight modification to the flux transfer device and no modification to the electronic trip circuit.